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INVITED REVIEW
  • Yoshinori Kanayama
    Type: Invited Review
    Volume 86 (2017) Issue 4 Pages 417-425
    Released: October 25, 2017
    [Advance publication] Released: January 31, 2017
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    Sugars are strongly related to fruit yield and quality, playing a critical role in fruit set, growth, ripening, and composition. The tomato (Solanum lycopersicum) is not only an important horticultural crop, but also a useful experimental model plant that can be used to further our understanding of fruit physiology. Therefore, in this review, we consider sugar metabolism and fruit development in the tomato. We begin by discussing how the sugar content of tomato fruit has been successfully increased in a tomato introgression line containing a chromosome segment from a wild relative, and how this has furthered our understanding of the mechanism controlling sugar content. We then outline current knowledge around how sugar sensing and signaling, proton pumps, and auxin affect sugar accumulation and fruit set. The prevention of fruit abscission by auxin, which is transported by PIN auxin efflux carriers and vacuolar proton phyrophosphatase (V-PPase), may retain sucrose transport to the fruit to inhibit programed cell death (PCD) and ensure successful fruit set. There is believed to be a trade-off between fruit sugar content and yield. However, fruit size and yield do not appear to decrease in the tomato introgression line IL8-3 and sucrose-induced repression of translation (SIRT)-engineered tomatoes, which contain higher fruit sugar contents. Future research needs to investigate the factors involved in sugar sensing and signaling, in addition to the sugar metabolic enzymes that have previously been studied for horticultural applications.

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ORIGINAL ARTICLES
  • Yutaka Sawamura, Yuko Suesada, Toshihiko Sugiura, Hideaki Yaegaki
    Type: Original Articles
    Volume 86 (2017) Issue 4 Pages 426-436
    Released: October 25, 2017
    [Advance publication] Released: January 20, 2017
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    A major goal of peach breeding programs in Japan is to develop cultivars with lower chilling requirements than the leading cultivars. Low-chill cultivars can be grown in subtropical as well as temperate regions. We investigated the chilling requirements (chill units; CU), heat requirements (growing degree hours; GDH), and blooming dates of 7 leading Japanese peach cultivars, 3 subtropical low-chill cultivars, and a promising new selection, Momo Tsukuba 127. In general, the CU of the 7 leading cultivars were higher than those of the 3 subtropical cultivars and Momo Tsukuba 127. The chilling and heat requirements were determined for the 3 leading high-chill cultivars (‘Akatsuki’, ‘Hikawahakuhou’, and ‘Kawanakajimahakutou’), the low-chill cultivar ‘Okinawa 1’, and Momo Tsukuba 127 during 4 seasons at a single location. The CU for ‘Okinawa 1’ and Momo Tsukuba 127 were significantly lower than those of the three high-chill cultivars. Because Momo Tsukuba 127 had lower chilling requirements than the 7 leading peach cultivars but higher chilling requirements than the subtropical cultivars, we classified this new selection as a mid-chill variety. We used the CU and GDH, along with local temperature data, to estimate the blooming dates of 4 cultivars and the new selection during 11 seasons at one location. Regression analyses showed high correlations between the calculated and actual blooming dates. We also compared calculated and actual blooming dates for the 3 leading cultivars and Momo Tsukuba 127 at between17 and 21 locations per genotype. A total of 25 locations were used, and these were widely spread over the temperate zones of Japan. The correlations between the calculated and actual blooming dates were close to 1:1. Our results indicated that our CU and GDH values, along with actual temperature data, could be used to reliably estimate the blooming dates of the genotypes. Because of its lower chilling requirements, the new selection, Momo Tsukuba 127, bloomed 7 or more days earlier than the leading peach cultivars in this study.

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  • Kazuya Ohata, Yasuyuki Togano, Toshikazu Matsumoto, Yoshinori Uchida, ...
    Type: Original Articles
    Volume 86 (2017) Issue 4 Pages 437-446
    Released: October 25, 2017
    [Advance publication] Released: January 31, 2017
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    Prune trees (Prunus domestica L.) are optimally suited to dry climates, and a major production area for prune trees is California, which has little rainfall. The East Asian temperate monsoon zone, where summer is hot and rainfall is relatively abundant, is not well suited for cultivating prune trees. The purpose of this study was to investigate prune cultivars that are ideal for this temperate monsoon zone to expand the possibility of production. We evaluated the performance of 8 prune cultivars, ‘Puchull’, ‘Purple Ais’, ‘Blue Tan’, ‘Edwards’, ‘Stanley’, ‘Valor’, ‘President’, and ‘Marjorie’s Seedling’, by harvesting fruits from August to October to identify optimal cultivars in Izumo, western Japan, as a model area in the temperate climate monsoon zone. Results showed that the flowering period of prune trees was from late March to mid-April, and average temperature in March influenced whether flowering time would occur early or late. The flowering period varied by year. Therefore, companion planting with other cultivars that have overlapping flowering periods is necessary for self-incompatible cultivars. To avoid spring frost damage during the flowering period, protection from frost was necessary. Additionally, to avoid fruit cracking, cultivating prune trees under rain shelter conditions was also necessary. With these management approaches, two mid-ripening types, ‘Stanley’ and ‘Valor’, and two late-ripening types, ‘President’ and ‘Marjorie’s Seedling’, yielded over 1000 kg/10 a/canopy area and produced high-quality fruit with over 20 soluble solids content (SSC)/titratable acid (TA). However, three early-ripening types, ‘Puchull’, ‘Purple Ais’, and ‘Blue Tan’, and the mid-ripening ‘Edwards’, showed relatively low yields and produced fruit with low SSC/TA. Moreover, flesh darkening before harvest was observed as a result of high-temperature injury in these cultivars, and skin color and fruit taste were not good enough before flesh darkening; thus, these four cultivars were not suitable for table use. In summary, we consider mid- to late-ripening cultivars suitable for table use in Izumo. Our findings also indicate the possibility that these prune fruit cultivation methods could be used in other parts of the East Asian temperate monsoon and humid temperate climate zone.

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  • Xi Li, Akira Kitajima, Keiko Kataoka, Rihito Takisawa, Tetsuya Nakazak ...
    Type: Original Articles
    Volume 86 (2017) Issue 4 Pages 447-455
    Released: October 25, 2017
    [Advance publication] Released: January 25, 2017
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    Histological investigations of the fruit abscission zone and morphological changes in abscission zone cells in ponkan (C. reticulata Blanco), hyuganatsu (C. tamurana hort. ex Tanaka), ‘Kiyomi’ (C. unshiu × C. sinensis (L.) Osbeck), and satsuma mandarin (Citrus unshiu Marcow.) were conducted using detached fruits incubated in agar medium under 25°C, 4 weeks after anthesis during secondary physiological fruit drop. In the 96 h after the fruit abscission induction by detaching the fruits, the cumulative abscission ratio was 100% in ponkan, 22% in ‘Kiyomi’, and below 10% in hyuganatsu and satsuma mandarin. Fruit abscission began at 36 h in ponkan and ‘Kiyomi’, at 54 h in satsuma mandarin, and at 60 h in hyuganatsu after the fruit detachment. The fruit abscission zone was located on the connected part between the fruit and the disc in ponkan and hyuganatsu on the disc tissue in satsuma mandarin and ‘Kiyomi’. During the fruit abscission process, no abscission layer was observed at the abscission zone in these species and cultivars. Morphological changes in the abscission zone cells were determined by scoring cell changes (a score from 0 to 4) at five positions of the abscission zone. In ponkan, the morphological changes in the abscission zone cells, which began 30 h after fruit abscission induction, were synchronized in a symmetrical position in the abscission zone. The changes in ‘Kiyomi’ began at 30 h, and they consisted of a one sided collapse of the symmetrical position of the abscission zone. The changes in satsuma mandarin were similar to those in ‘Kiyomi’. This implies that the different patterns of morphological changes in the abscission zone cells in ponkan, ‘Kiyomi’, and satsuma mandarin depend on the different locations of their abscission zones. Overall, the results suggest that the cue for fruit abscission in early abscised fruit occurs until 30 h after blocking the carbohydrate translocation to the fruit under 25°C.

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  • Norio Takada, Masahiko Yamada, Sogo Nishio, Yutaka Sawamura, Akihiko S ...
    Type: Original Articles
    Volume 86 (2017) Issue 4 Pages 456-462
    Released: October 25, 2017
    [Advance publication] Released: February 28, 2017
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    The pellicle of the Japanese chestnut (Castanea crenata Sieb. et Zucc.) is difficult to peel, with the exception of the recently developed ‘Porotan’, whose pellicle peelability (PP) is high and controlled by a single major gene. The objective of the present study was to identify any genetic differences in PP in Japanese chestnuts with difficult-peeling pellicles. We detected a significant genetic difference in PP (evaluated as the nut surface area that peeled away without scraping with a hand knife after deep frying in cooking oil) among five Japanese chestnut cultivars grown in Tsukuba, Japan, using two trees in 2 years, and among three cultivars grown in five locations using a single tree in 1 year. We evaluated the PP of 32 Japanese chestnut cultivars/selections and one wild clone (Shibaguri-37) using a single tree in 3 years to quantify the variation. The broad-sense heritability of mean values over the 3 years was estimated as 0.67. Shibaguri-37 had the highest PP. The suggested new genes controlling the variation in PP have high potential in terms of breeding strategy for easy-peeling pellicles as an alternative to the major gene of ‘Porotan’, the use of which is likely to result in inbreeding.

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  • Atsu Yamasaki, Hiroshi Yakushiji, Hajime Iwamoto, Akifumi Azuma, Hiroy ...
    Type: Original Articles
    Volume 86 (2017) Issue 4 Pages 463-469
    Released: October 25, 2017
    [Advance publication] Released: March 17, 2017
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    Various on-tree ethanol-sticker treatments for ‘Taigetsu’ and ‘Taiten’ persimmon (astringent cultivars) were tested to identify optimal treatment conditions for astringency removal and fruit quality. Using aluminum foil coated or polyethylene terephthalate stickers to attach a pad containing 1.5 g of ethanol powder to both sides of the fruit surface in early October removed astringency completely, while the application of treatments to one side of the fruit surface did not. The astringency removal was incomplete in treatments with a cast coating sticker. The aluminum foil-coated sticker with a 1.0 g ethanol pad applied in early October removed flesh astringency completely without fruit skin darkening or the occurrence of large numbers of brown specks in the flesh. It extended fruit shelf life by approximately 7 days compared with postharvest CO2 treatment in November. Conversely, sticker treatments in late September caused many brown specks in the flesh. The sticker treatment with a 0.6 g ethanol pad failed to remove the astringency completely while the sticker treatment with a 1.5 g ethanol pad resulted in heavy fruit skin darkening or the appearance of shallow concentric cracks on the fruit skin. Therefore, we conclude that an on-tree sticker treatment with a 1.0 g ethanol pad on both sides of the fruit surface in early October removes fruit astringency completely and provides high quality ‘Taigetsu’ and ‘Taiten’ persimmon fruit.

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  • Ken Takahata
    Type: Original Articles
    Volume 86 (2017) Issue 4 Pages 470-478
    Released: October 25, 2017
    [Advance publication] Released: January 07, 2017
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    The objective of this study was to determine whether planting pepino (Solanum muricatum Ait.) cuttings (shoots have 5 or 6 true leaves and length is 5–6 cm) through the hole (diameter is 4 mm) of a steel washer (hereinafter referred to as the “washer ring treatment”) would increase the soluble solids content of pepino fruit. Experiments were conducted twice: i.e. from spring to summer (Experiment 1) and from autumn to spring (Experiment 2). The washer ring treatment caused marked increases in stem diameter immediately above the washer compared to the control, but slightly suppressed stem elongation and leaf unfolding. The stem diameter above the washer at the end of culture was smaller in the treated plants compared to the control plants. The fresh weights of both above-ground and root tissues were also smaller in the treated plants compared with control plants. In contrast, no differences were observed between the treated and control plants in the number of flowers, the fruit set ratio, or the disorder fruits ratio. The marketable fruits harvested from treated plants were smaller compared to those from control plants by 28 to 47 g and 66 to 147 g in Experiments 1 and 2, respectively (i.e. reduction in yield); however, the fruits were denser and contained more soluble solids at 1.1 to 2.4°Brix and 1.1 to 2.9°Brix, respectively. This study confirmed that the washer ring treatment is effective for increasing the soluble solids content of pepino fruit.

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  • Sota Koeda, Kanami Homma, Yuri Tanaka, Elly Kesumawati, Sabaruddin Zak ...
    Type: Original Articles
    Volume 86 (2017) Issue 4 Pages 479-486
    Released: October 25, 2017
    [Advance publication] Released: January 07, 2017
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    Tomato yellow leaf curl disease caused by begomoviruses is a serious threat to tomato (Solanum lycopersicum L.) production. If begomoviruses, transmitted by whitefly (Bemisia tabaci), infect tomato plants during early growth, production can be almost entirely lost. Tomato yellow leaf curl Kanchanaburi virus (TYLCKaV), a bipartite Begomovirus, is emerging as an important threat to solanaceous crop production in Southeast Asia. The lack of mechanical transmission of some begomoviruses is a major experimental constraint. In this study, an agroinoculation method using TYLCKaV in tomato plants was established. Partial tandem repeats of TYLCKaV DNA A and DNA B were constructed and cloned to a binary pGreenII vector, and their infectivity was tested. Co-inoculation of TYLCKaV DNA A and DNA B to Nicotiana benthamiana L. produced typical begomoviral symptoms, and both of the viral DNA components accumulated in the upper uninoculated leaves, suggesting systemic infection of TYLCKaV. Two agroinoculation methods were conducted on tomatoes. First, excised sections of tomato shoots were agroinoculated with a soaking procedure. Although two Agrobacterium tumefaciens strains were tested, approximately 40% of inoculated plants only showed viral symptoms for EHA105. Second, agrobacterium from a cultured petri dish was directly inoculated with a colony inoculation procedure. When EHA105 was used, approximately 92% of inoculated plants showed viral symptoms. Sequencing the recovered viral DNA from the upper uninoculated leaf clarified that TYLCKaV had successfully infected the tomato plants. The colony inoculation procedure is labor-saving, and viral symptoms develop in susceptible tomato plants within approximately a month from sowing the seeds. This method could contribute to simple and speedy evaluation of TYLCKaV resistance of tomato plants.

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  • Rihito Takisawa, Takayuki Maruyama, Tetsuya Nakazaki, Keiko Kataoka, H ...
    Type: Original Articles
    Volume 86 (2017) Issue 4 Pages 487-492
    Released: October 25, 2017
    [Advance publication] Released: March 03, 2017
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    Parthenocarpy is a trait where fruit set and growth are triggered without pollination and fertilization. In the tomato (Solanum lycopersicum L.), this trait is considered attractive as it reduces the cost and labor requirements for fruit setting. In this study, we investigated the inheritance of parthenocarpy in ‘MPK-1’—a parthenocarpic tomato cultivar derived from a cross between a variant from a self-fertilization posterity of ‘Severianin’, which exhibited strong parthenocarpy and a non-parthenocarpic cultivar. It was reported that ‘MPK-1’ contains a pat-2 gene because ‘Severianin’ which has a pat-2 gene is its only parthenocarpic ancestor. However, we found that parthenocarpy in ‘MPK-1’ is controlled by a novel parthenocarpic gene, not pat-2. This novel gene, which was designated as Pat-k, is semi-dominant and located on chromosome 1. We also showed that the size of the parthenocarpic fruit of ‘MPK-1’ is similar to that of the pollinated fruit at maturity. Thus, ‘MPK-1’ may be used as a new parthenocarpic resource for breeding.

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  • Rafael Alexandre Muchanga, Toshiyuki Hirata, Hajime Araki
    Type: Original Articles
    Volume 86 (2017) Issue 4 Pages 493-500
    Released: October 25, 2017
    [Advance publication] Released: April 18, 2017
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    In order to establish a low-input alternative production system based on cover crops, the effectiveness of hairy vetch (Vicia villosa Roth; HV) incorporated as a basal nitrogen fertilizer and its effects on soil carbon (C) and nitrogen (N) content in fresh-market tomato production in plastic high tunnel was investigated in Sapporo (snow cover region), Japan. The treatments consisted of HV seeding rates (HV2, 2 kg/10 a; HV5, 5 kg/10 a) and ammonium sulfate (AS10, 10 kg N/10 a) applied as basal N fertilizers, and the Non HV (control) with no HV and ammonium sulfate. In all plots, 15 kg N/10 a were added before tomato transplanting as a controlled-release fertilizer (LPS100 41%−N) to maintain the tomato growth in the mid and late stages. HV aboveground biomass (dry weight) was 585 kg/10 a in HV2 and 719 kg/10 a in HV5. Nitrate in petiole sap was higher in HV2, HV5, and AS10 plots than in Non HV plots throughout the cultivation period with the exception of the first 2 weeks after transplanting (WAT). The Growth index (GI) was higher in HV2 (47971), HV5 (46285), and AS10 (43397) than in Non HV (39847) at 7 WAT, the beginning of the harvest. Higher marketable yields were found in tomatoes grown in HV2 (6.87 t/10 a), HV5 (6.91 t/10 a), and AS10 (6.08 t/10 a), compared with the Non HV (5.19 t/10 a). The HV plots had greater soil total and organic N than AS10 and Non HV, and slightly increased soil C after tomato production. From these results, the HV seeding rate of 2 kg/10 a will be enough to support the growth of tomatoes planted after HV production if HV grows steadily in a plastic high tunnel.

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  • Tomoo Maeda, Ayumi Watanabe, Daniel Zadrak Wambrauw, Sachiyo Osanai, K ...
    Type: Original Articles
    Volume 86 (2017) Issue 4 Pages 501-510
    Released: October 25, 2017
    [Advance publication] Released: March 29, 2017
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    Onions (Allium cepa L.) accumulate fructo-oligosaccharides (FOSs) as storage carbohydrates. FOSs exist in various chemical forms with different degrees of polymerization (DP) and chemical bonding states. Therefore, it is difficult to determine the precise FOS composition and quantity of each type of FOS. The objective of this study was to analyze the varietal differences in FOS composition and relative quantities among onion cultivars grown by spring-sown cultivation in Hirosaki City, Japan, using a high performance liquid chromatography (HPLC) system equipped with an evaporative light scattering detector (ELSD). FOS compositions of a number of varieties, as determined by HPLC/ELSD, were confirmed using matrix-assisted laser desorption/ionization time-of-flight -mass spectrometry (MALDI-TOF MS). Sugar and FOS analyses revealed distinct patterns of sugar and FOS accumulation, which led to categorization of the tested varieties into three types: (1) those with a relatively high overall quantity of FOSs and with a higher DP (DP3 to over DP9); (2) those containing mainly monosaccharides (fructose and glucose), disaccharide (sucrose), and low amounts of FOSs; and (3) those with a carbohydrate content that was intermediate compared to that of the other two types. Measurements of enzyme activities suggested that varietal differences in FOS composition are the result of differences in enzyme activities associated with the FOS biosynthetic and biodegradation pathways.

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  • Chengyao Jiang, Masahumi Johkan, Masaaki Hohjo, Satoru Tsukagoshi, Mit ...
    Type: Original Articles
    Volume 86 (2017) Issue 4 Pages 511-518
    Released: October 25, 2017
    [Advance publication] Released: April 18, 2017
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    Tomato plants in greenhouse production are often confronted with light insufficiency in the lower canopy, especially in the winter low irradiation season. In this study, periodic alteration of plant density (PD) was proposed to improve the light environment of plants’ lower canopies, leaf photosynthesis, plant growth, and fruit development. These were investigated with winter cultivated tomatoes in a single-truss production system. Seedlings were transplanted to either movable or fixed cultivation benches for treatments with fixed PDs of 14.3 plants·m−2 (F14.3), and 10 plants·m−2 (F10), and unfixed PDs in a movable bench (MB; 25 plants·m−2 after transplanting to anthesis, 16.6 plants·m−2 at anthesis to initial fruit set, 12.5 plants·m−2 at fruit set to mature green, and 11.1 plants·m−2 at mature green to red-ripe). The leaf photosynthesis rates in MB and F10 were generally significantly higher than in F14.3. F14.3 had the tallest stems, but the lowest leaf area and shoot dry weight at end of experiment, while MB and F10 were not significantly different. MB had significantly the highest total yield, while the lowest data were observed in F10. The soluble solids content was increased in MB and F10 compared with F14.3, but no significant differences in ascorbic acid content or fruit hardness were observed among treatments. Therefore, a high PD in the vegetative stage, but a relatively lower PD in the fruit development stage, was highly efficient in intensive tomato cultivation.

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  • Shigeto Morita, So Sugiyama, Yoshihiro Nomura, Takehiro Masumura, Shig ...
    Type: Original Articles
    Volume 86 (2017) Issue 4 Pages 519-527
    Released: October 25, 2017
    [Advance publication] Released: February 22, 2017
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    2,4-Pyridinedicarboxylic acid (2,4-PDCA) extends the vase life of cut flowers of spray-type carnations by accelerating flower opening as well as retarding senescence. Since 2,4-PDCA can inhibit 2-oxoglutarate-dependent dioxygenases, which include enzymes for gibberellin (GA) biosynthesis and catabolism, we hypothesized that GA might be involved in the enhancing effect of 2,4-PDCA on the flower opening of carnation. In this study, we tested this possibility by examining the changes in gene expression of DELLA protein (GAI), a negative regulator of GA signaling, and GA levels in carnation (Dianthus caryophyllus L. ‘Light Pink Barbara (LPB)’) flowers treated with 2,4-PDCA. We also analyzed the expression of cell expansion-related genes, xyloglucan endotransglucosylase/hydrolase (XTH), and expansin genes as markers of flower opening in the treated flowers. The transcript level of GAI gene was increased, whereas that of expansin was decreased, in petals of the 2,4-PDCA-treated flowers compared to those of the control, which was contrary to the enhancement of flower opening. Our results suggest that the changes in the expression of these genes are not associated with the enhancing effects of 2,4-PDCA. In addition, GA3 content tended to be decreased by 2,4-PDCA treatment in the petals of opening flowers. Flower opening was not accelerated, but rather delayed, by treatment of flower buds with exogenous GA3 and not affected by paclobutrazol, an inhibitor of GA biosynthesis, in ‘LPB’ carnation. These results suggest that endogenous GA is not associated with the enhancement of flower opening by 2,4-PDCA in carnation.

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  • Masumi Yamagishi, Takashi Nakatsuka
    Type: Original Articles
    Volume 86 (2017) Issue 4 Pages 528-533
    Released: October 25, 2017
    [Advance publication] Released: February 28, 2017
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    Genes encoding a MYB12 transcription factor, which regulates anthocyanin biosynthesis, are the key genes causing variations in the anthocyanin colors in lily flowers. However, the origin of the MYB12 in Asiatic hybrid lilies (Lilium spp.) is not completely known. In this study, we analyzed anthocyanin pigments in tepals of L. maculatum, L. lancifolium, L. callosum, L. leichtlinii, L. davidii, L. bulbiferum, and L. dauricum, and clarified that L. dauricum and L. bulbiferum accumulated a single anthocyanin, cyanidin 3-O-rutinoside, in entire tepals, although these wild species had orange-colored tepals. The sequencing of MYB12 genes revealed seven allelic sequences among ten L. dauricum plants and two allelic sequences in one L. bulbiferum plant. These MYB12 sequences were the same as or similar to the sequences isolated from pink Asiatic hybrid lily cultivars, indicating that L. dauricum and L. bulbiferum have contributed to the anthocyanin coloration of these cultivars.

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  • Mari Sugiyama, Takuya Katsube, Akio Koyama, Hiroyuki Itamura
    Type: Original Articles
    Volume 86 (2017) Issue 4 Pages 534-542
    Released: October 25, 2017
    [Advance publication] Released: January 19, 2017
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    The aim of this study was to determine the best time to harvest mulberry (Morus alba L.) leaves for optimal yields of functional components. Mulberry leaves were analyzed to determine the seasonal changes in the concentrations of functional components, including flavonols, chlorogenic acid, and 1-deoxynojirimycine (DNJ). During the experimental period (May 26–October 16), the ranges of flavonols, chlorogenic acid, and DNJ contents were 1134–2230 mg/100 g dry weight (DW), 616–1014 mg/100 g DW, and 53–199 mg/100 g DW, respectively. There were high flavonols contents in mulberry leaves from late May to early July, from early to mid-August, and after late September. There were high chlorogenic acid contents from late May to early July, and after late September. From late September, the flavonols contents increased over time, and showed the highest level on October 16, the last day of the experimental period. The increased flavonols contents after late September were due to the synergistic effects of solar radiation and lower temperatures. The DNJ content showed a bell-shaped curve, peaking in mid-August, and the DNJ content was strongly correlated with total temperature. The flavonols and chlorogenic acid contents in mulberry leaves were higher after late September when the temperatures decreased and there was still high solar radiation, while the DNJ content peaked in August when temperatures were highest. The results indicated that August is the best time to harvest mulberry leaves to obtain optimal yields of beneficial functional components. If mulberry leaves are harvested twice per year, then the first harvest should be in July to August when temperatures and solar radiation hours are high, and the second harvest should be completed by the end of September.

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  • Yuta Kimura, Mari Naeshiro, Yuri Tominaga, Toyoaki Anai, Fuminori Koma ...
    Type: Original Articles
    Volume 86 (2017) Issue 4 Pages 543-551
    Released: October 25, 2017
    [Advance publication] Released: January 25, 2017
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    ‘Sagan-Ruby’ is the first grapefruit (Citrus paradisi) cultivar to be developed in Japan and is used for food, cosmetics, and other purposes owing to its favorable characteristics, such as the absence of harmful pesticides and its long shelf life. The desired qualities of grapefruit depend on the specific use, and these qualities are influenced by the metabolite composition of the fruits. However, little is known about the influence of the growing environment or harvest period on the metabolite composition of the ‘Sagan-Ruby’ grapefruit. Therefore, we harvested fruits that were grown either in a plastic house without artificial heating or outdoors with rain cover from December, 2014 to April, 2015, on a monthly basis, and we investigated the composition of the primary metabolites such as sugars, organic acids, and amino acids, in the juice and peel of the fruit using gas chromatography mass spectrometry (GC/MS). We detected a total of 53 and 68 compounds in the juice and peel, respectively, and the first and second components of the principal component analyses of the detected metabolites of both juice and peel were associated with the growing environment and harvest period, respectively. Since we observed that glucose, fructose, sucrose, and citric acid were more concentrated in the juice of outdoor-grown fruits than in that of the house-grown fruits, especially in March and April, it is likely that the sweetness and acidity of the fruits are dependent on the growing environment. Similarly, the primary metabolite contents, including succinic acid and other organic acids, were higher in peels from outdoor-grown fruits. In addition, we also observed that the contents of proline, phenylalanine, and other amino acids in the juice increased continuously from December to April, and many sugars, including glucose and fructose, gradually decreased in peels from December to February and were lower from February to April. These results indicated that quality of the ‘Sagan-Ruby’ grapefruit varies with the harvest period.

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